Essential plant nutrients include primary nutrients, secondary or macronutrients, and trace or micronutrients. Primary nutrients include carbon, hydrogen, oxygen, nitrogen, phosphorous, and potassium. Carbon and oxygen are absorbed from the air, while other nutrients including water (source of hydrogen), nitrogen, phosphorous, and potassium are obtained from the soil. Fertilizers containing sources of nitrogen, phosphorous, and/or potassium are used to supplement soils that are lacking in these nutrients.
According to the conventional fertilizer standards, the chemical makeup or analysis of fertilizers is expressed in percentages (by weight) of the essential primary nutrients nitrogen, phosphorous, and potassium. More specifically, when expressing the fertilizer formula, the first figure represents the percent of nitrogen expressed on the elemental basis as “total nitrogen” (N), the second figure represent the percent of phosphorous expressed on the oxide basis as “available phosphoric acid” (P2O5), and the third figure represents the percent of potassium also expressed on the oxide basis as “available potassium oxide” (K20), or otherwise known as the expression (N—P2O5—K2O).
Even though the phosphorous and potassium amounts are expressed in their oxide forms, there is no P205 or K20 in fertilizers. Phosphorus exists most commonly as monocalcium phosphate, but also occurs as other calcium or ammonium phosphates. Potassium is ordinarily in the form of potassium chloride or sulfate. Conversions from the oxide forms of P and K to the elemental expression (N—P—K) can be made using the following formulas:%P=%P205×0.437%K=%K20×0.826%%P205=%P×2.29%K20=%K×1.21
Muriate of potash (MOP), otherwise known as potassium chloride, KCl, is an agricultural fertilizer, and is the most common source of fertilizer potassium. MOP by definition contains 48% to 62% soluble K2O, mainly as chloride. MOP is typically extracted from naturally occurring underground mineral sources either by conventional mining or solution mining techniques. Once extracted, MOP can be processed into a number of different finished forms or KCl products suitable for specific industrial, chemical, human or animal nutrients or agricultural applications as desired by individual customers.
Finished MOP, for the purpose of agricultural consumption, is typically sold in a granular form. The purity and granule size may vary depending on the end use to which the product will be put. The granules are produced using crushing and sizing processes known to one of ordinary skill in the art, such as by compaction and the subsequent crushing and sizing which thereby break up the larger pieces of MOP into smaller granules. Compaction implies the continuous rolling of MOP feed material at elevated pressures yielding cohesion of material in the resultant product. The grading of MOP, and hence its market value, is also dependent on both the purity and granule size of the product. Typically the MOP is screened to the desired particle size for a particular need.
A typical MOP feed stock has a granule size that is comparable to table salt, which is less than the desired granule size. In order to obtain larger granules, this feedstock is first compacted using a compacting process such as a simple roll compacter or the like to produce a sheet-like cohered product. Subsequent processing typically involves controlled breakage of the MOP sheet into granules, which are then sorted to a desired size range by screening or other classification methods known in the industry. A non-limiting example of a standard industry known roll compactor is K.R. Komarek's B220B Compactor (or any of the “B” models or high pressure briquetting and compacting machines) available from K.R. Komarek, Inc. of Wood Dale, Ill.
In addition to the primary nutrients, such as potassium that is made available to plants via the MOP fertilizer added to soil, micronutrients and secondary nutrients are also essential for plant growth. These are required in much smaller amounts than those of the primary nutrients. Secondary nutrients can include, but are not limited to, sulfur (SO4), calcium (Ca), magnesium (Mg) or combinations thereof. Micronutrients can include, but are not limited to, for example, boron (B), zinc (Zn), manganese (Mn), nickel (Ni), molybdenum (Mo), copper (Cu), iron (Fe), chlorine (Cl), or combinations thereof. From this point forward and throughout the specification, for the sake of simplicity, the term “micronutrient” refers to and includes both secondary nutrients and micronutrients.
A common method of micronutrient application for crops is soil application. Recommended application rates usually are less than 10 lb/acre on an elemental basis. Separate micronutrient applications at these low rates are difficult and are prone to result in the poor uniformity of distribution. Including micronutrients with mixed fertilizers is a convenient method of application and some methods allow more uniform distribution with conventional application equipment. Costs also are reduced by eliminating a separate application step. Four methods of applying micronutrients with mixed fertilizers can include incorporation during manufacture, bulk blending with granular fertilizers, coating onto granular fertilizers and seeds, and mixing with liquid herbicides or fluid fertilizers.
Bulk blending with granular fertilizers is the practice of bulk blending micronutrient compounds with phosphate, nitrogen and potash fertilizers. The main advantage to this practice is that fertilizer grades can be produced which will provide the recommended micronutrient rates for a given field at the usual fertilizer application rates. The main disadvantage is that segregation of nutrients can occur during the blending operation and with subsequent handling. Micronutrients are often small in particle size which can result in segregation in a bulk blend. In order to reduce or prevent size segregation during handling and transport, the ideal micronutrient granules must be close to the same size as the phosphate, nitrogen and potash granules. Because the micronutrients are required in very small amounts for plant nutrition, this practice has resulted in granules of micronutrients unevenly distributed and generally too far from most of the plants to be of immediate benefit as most micronutrient elements migrate in soil solution only a few millimeters during an entire growing season.
Coatings decrease the possibility of segregation. However, some surface binding materials are unsatisfactory because they do not maintain the micronutrient coatings during bagging, storage, and handling, which results in segregation of the micronutrient sources from the granular fertilizer components.
Steps have been taken to reduce the segregation problem for example as in the case of sulfur or sulfur platelets in the fertilizer portion as described in U.S. Pat. No. 6,544,313 entitled “Sulfur-Containing Fertilizer Composition and Method for Preparing Same” and in the case of micronutrients as described in U.S. Pat. No. 7,497,891 entitled, “Method for Producing a Fertilizer with Micronutrients,” both of which are incorporated by reference in their entireties. This preparation method, however, is directed to a granulation process.
Some micronutrient pelletizing and compaction applications exist in such products as sodium chloride (salt) and kieserite (magnesium sulfate monohydrate); however the inclusion of micronutrients into a primary nutrient, such as MOP, using a roll compactor is not known in the prior art to the inventors' knowledge.
Micronutrient addition has historically been performed in downstream operations outside the processing boundaries of MOP miners and millers. There is a well-documented long term need to increase crops yields in order to feed an ever-increasing world population. Therefore, there remains a need to economically create a compacted, crushed and sized, granular MOP value-added fertilizer product that contains one or more micronutrients that maximizes the introduction of the micronutrient(s) into soil solution and ultimately to the root zone of plants.